1. Field of the Invention
The present invention relates to a liquid crystal display device and a driving method thereof, and more particularly to a liquid crystal display device and a driving method thereof which prevents an abnormal phenomenon on a screen.
2. Description of the Related Art
Mobile information devices include flat panel display devices because they are light weight with minimal thickness. In particular, a liquid crystal display device is actively used in a notebook, a monitor of a desktop computer, a television, and the like. The liquid crystal display device displays images by using an optical anisotropy of a liquid crystal and provides good performance in resolution, color display, and image quality.
FIG. 1 shows a liquid crystal display device 50 which includes a liquid crystal panel 2, a gate driver 4, a data driver 6 and a timing controller 10. The liquid crystal panel 2 arranges a plurality of liquid crystal cells in a matrix shape defined by a plurality of gate lines GL1-GLn and a plurality of data lines DL1-DLm. The gate driver 4 applies gate scan signals to the gate lines GL1-GLn of the liquid crystal panel 2. The data driver 6 applies pixel signals to the data lines DL1-DLm of the liquid crystal panel 2. The timing controller 10 controls the gate driver 4 and the data driver 6.
The liquid crystal panel 2 includes a plurality of the liquid crystal cells which are defined by a plurality of the gate lines GL1-GLn and a plurality of the data lines DL1-DLm, and thin film transistors (TFTs). The TFTs are formed in each of the liquid crystal cells and are connected to the gate lines GL1-GLn and the data lines DL1-DLm.
When a scan signal, for instance, a gate high voltage (Vgh) is provided from the gate lines GL1-GLn, the TFTs are turned on and provide pixel signals applied from the data lines DL1-DLm to the liquid crystal cells. On the other hand, when a gate low voltage (Vg1) is provided from the gate lines GL1-GLn, the TFTs are turned off and maintain the pixel signals charged in the liquid crystal cells.
Each liquid crystal cell is associated with a pixel electrode and a common electrode facing each other. The pixel electrode is connected to a TFT and stores a pixel signal, thereby forming a liquid crystal capacitor Clc. In addition, a storage capacitor Cst is formed in the liquid crystal cell to maintain the pixel signal in a stable manner until the next pixel signal is charged after one pixel signal is charged. With such a configuration, the liquid crystal display device 50 may change an array state of liquid crystal molecules having dielectric anisotropy according to the pixel signals inputted through the TFTs, and may implement a gradation by adjusting the light transmissivity according to the array state of the liquid crystal molecules.
As the timing controller 10 sends gate control signals, the gate driver 4 sequentially outputs gate high voltages (Vgh) to the gate lines GL1-GLn and drives each of the TFTs connected to the gate lines GL1-GLn. As the timing controller 10 sends data control signals, the data driver 6 outputs pixel signals to the data lines DL1-DLm. The data driver 6 converts digital signals of R, G, and B provided by the timing controller 10 into analog pixel signals, and then provides the converted signals to the data lines DL1-DLm.
The TFTs are turned on for a determined period of time upon application of the gate high voltages Vgh. In a state that the TFTs are turned on, the pixel signals in the data driver 6 are applied to the data lines DL1-DLm through the TFTs.
At the time of the initial driving of the liquid crystal display device 50, the TFTs may not be completed turned off for a short period of time. The tail of the waveforms may keep the TFTs turned on before the TFTs are completely turned off. A certain initial data, which is arbitrarily set by driver manufacturers, may be provided to the data lines DL1-DLm. The initial data are further applied to the liquid crystal cells and a screen displays an image corresponding to the initial data. Upon application of a picture signal of a gradation voltage, the prolonged on-state of the TFTs may affect a screen quality. A stripe, which is visually recognizable, may occur on the screen for a short time. Therefore, there is a need for a liquid crystal display device that overcomes such drawback of the related art.